NGPre WASM tile source: assume we only deal with a single channel

Therefore, the size of a block is now reported as an array of the form
[x, y, z], including no channel information anymore.

Having a 4D array as size, lead to different problems in the front-end.

Author: tomka

django/applications/catmaid/static/js/tile-source.js

@@ -754,7 +754,7 @@
             .then(block => {
               if (block) {
                 let etag = block.get_etag();
-                let size = block.get_size(); // [x, y, z, channel]
+                let size = block.get_size(); // [x, y, z]
                 let n = 1;
                 let stride = size.map(s => { let rn = n; n *= s; return rn; });
                 return {
@@ -1195,7 +1195,7 @@
             block = block_data[i];
             if (block) {
               let etag = block.get_etag();
-              let size = block.get_size(); // [x, y, z, channel]
+              let size = block.get_size(); // [x, y, z]
               let gridPosition = block.get_grid_position();
               let n = 1;
               let stride = size.map(s => { let rn = n; n *= s; return rn; });

django/applications/catmaid/static/libs/ngpre-wasm/ngpre_wasm_worker.js

@@ -40,7 +40,9 @@ onmessage = function(e) {
                 // transferrable and therefore zero-copy.
                 loadedBlocks.push({
                   etag: block.get_etag(),
-                  size: block.get_size(),
+                  // We receive [x, y, z, ch] as size and expect only a single
+                  // channel at the moment.
+                  size: block.get_size().slice(0, 3),
                   gridPosition: block.get_grid_position(),
                   // Needs to be last, due to the block being consumed (into)
                   data: block.into_data(),
@@ -118,7 +120,9 @@ onmessage = function(e) {
             // transferrable and therefore zero-copy.
             let desBlock = {
               etag: block.get_etag(),
-              size: block.get_size(),
+              // We receive [x, y, z, ch] as size and expect only a single
+              // channel at the moment.
+              size: block.get_size().slice(0, 3),
               data: block.into_data(),
             };
             postMessage([messageId, desBlock], [desBlock.data.buffer]);